1. Field of the Invention
The present invention relates to a bumper reinforcement including a tow hook attachment structure and a method of manufacturing the bumper reinforcement.
2. Description of the Related Art
A bumper reinforcement, which is mounted in a front portion and/or a back portion of a vehicle body, includes a tubular body (bumper reinforcement body) having a hollow cross section and extending in the vehicle width direction. The tubular body has a front wall that serves as an impact surface and a rear wall on the vehicle body side. The bumper reinforcement absorbs impact energy and protects passengers in an automobile crash.
In recent years, crash safety standards for automobiles have been made stricter, and accordingly the strength of a bumper reinforcement has been increased. On the other hand, even under such circumstances, reduction of the cost of fuel and increase of the driving performance of automobiles have been required. Therefore, increase of the strength and reduction of the weight of a bumper reinforcement, which is an impact energy absorbing component, are both required. As the material of a bumper reinforcement, a press-formed plate or an extruded member of an aluminum alloy, a press-formed product or a roll-formed product of a high-tensile steel, or the like is used.
Such a bumper reinforcement has a tow hook attachment structure for allowing a removable tow hook to be attached thereto. The tow hook is used, for example, to tow the automobile or immobilize the automobile in a car carrying ship.
In general, a tow hook attachment structure includes a tow hook attachment member attached to the aforementioned tubular body. For example, a bumper reinforcement illustrated in FIG. 2 of Japanese Unexamined Patent Application Publication No. 2009-67188 includes a block-shaped tow hook attachment member that is attached to a front wall of a tubular body of the bumper reinforcement by, in this example, welding. When the automobile is to be towed, a tow hook is attached to the bumper reinforcement by screwing a threaded portion of the tow hook into a threaded hole formed in the tow hook attachment member.
In the existing bumper reinforcement described above, the tow hook attachment member is manufactured independently, and the tow hook attachment member is attached to the tubular body (bumper reinforcement body) by welding or by using a bolt and a nut or the like. In the case where the tow hook attachment member is attached by welding, it is necessary to increase the welding length in order to ensure sufficient endurance strength, because the tubular body may become softened by welding heat and the strength of a joint portion may be decreased. As a result, there is a problem of an increase in the weight and the manufacturing cost, because the welding cost is increased and the size of the tow hook attachment member is increased. In the case where the tow hook attachment member is attached by using a bolt and a nut or the like, it is necessary to increase the size of the tow hook attachment member and the number of components in order to provide a bearing surface for the bolt and the nut or the like. As a result, there is a problem of an increase in the weight and the manufacturing cost.